A. Field of Invention
This invention pertains to a method and apparatus for imbedding control signals in the visible portion of a video signal.
B. Description of the Prior Art
U.S. Pat. No. 4,807,031 in the name of Broughton, et al. that issued on Feb. 21, 1989 and is entitled “Interactive Video Method and Apparatus” discloses a method and apparatus for in-band, video broadcasting of commands to interactive devices. Control data is encoded into the video image using a “subliminal” modulation scheme, a scheme that can be detected electronically but is largely imperceptible to the viewer. The encoding is in a selected sequence of video image fields. The resulting modulated video fields are within the displayed area of the video (the area that is seen by the viewer), and have alternately proportionately raised and lowered luminance on selected horizontal scan lines. As disclosed in the patent, the modulation is monitored by a light sensitive device positioned adjacent the user's television screen.
The modulation of the video signal used by Broughton, et al. is referred to herein as “VEIL modulation”, VEIL being the commercial name of the system based on the patent. VEIL is simpler and easier to implement than watermarking technology in that the VEIL modulation can be sensed by looking for a single frequency in the video signal.
VEIL has been proven to work in standard definition television systems such as 525-line, 60 Hz interlaced (NTSC) and 625-line, 50 Hz interlaced (PAL). However, the introduction of new television systems such as the Advanced Television System Committee's Digital TV Standards which includes digital high definition television (HDTV), standard definition television (SDTV), data broadcasting, multi-channel surround-sound audio, and satellite direct-to-home broadcasting means that in the future video signals will be subjected to changes in resolution between the point of transmission and the display device.
The ATSC standard includes the standard definition resolutions such as 525i (the NTSC signal, 525 lines transmitted as an interlaced signal), and high definition resolutions such as 720p (720 lines transmitted as a progressive scan signal) and 1080i (1080 lines transmitted as an interlaced signal). Changing the resolution of a video signal is commonly referred to as “up res'ing” when the resolution of the video signal is increased and “down res'ing” when the resolution of the video signal is decreased.
VEIL encoding involves increasing the average luminance of one line in a field and decreasing the average luminance of the next adjacent line. There is no problem when up res'ing as will be explained below. However, if the video signal with the VEIL encoding is subjected to down res'ing, the VEIL encoded data may not be retrievable.
It is a general object of our invention to provide a form of VEIL modulation that can be detected even after down res'ing.
It is another object of our invention to provide VEIL modulation detection with the same notch filter and level detector no matter how the resolution is changed.